Method of making an electrode assembly for plasma processing apparatus

ABSTRACT

A method of making an electrode assembly for a plasma processing apparatus includes securing a backing member to an electrode wherein first fastener members mounted in apertures in the backing member cooperate with second fastener members to hold the electrode assembly to a support member, such as a temperature-controlled top plate in a plasma processing chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 10/623,540 entitled ELECTRODE ASSEMBLY FOR PLASMA PROCESSINGAPPARATUS, filed on Jul. 22, 2003 now U.S. Pat. No. 7,543,547, whichclaims the benefit of U.S. Provisional Application No. 60/400,451, filedJul. 31, 2002, the entire contents of each is hereby incorporated byreference.

BACKGROUND

Plasma processing apparatuses are used to process substrates bytechniques including etching, physical vapor deposition (PVD), chemicalvapor deposition (CVD), ion implantation, and resist removal. One typeof plasma processing apparatus used in plasma processing includes areaction chamber containing upper and lower electrodes. An electricfield is established between the electrodes to excite a process gas intothe plasma state to process substrates in the reaction chamber.

SUMMARY

A component for a plasma processing apparatus is provided. In apreferred embodiment, the component includes a first member bonded to asecond member. The first member includes a plurality of throughapertures, each having a first portion, and a wider second portion. Thecomponent also includes a plurality of first fastener members adapted tobe mounted in the apertures. The first fastener members preferablyinclude a bearing surface facing a surface at least partially definingthe second portion of the aperture.

In a preferred embodiment, the component is an electrode assembly.

In another embodiment, the electrode assembly is attached to a topplate. The top plate is mounted, or adapted to be mounted, inside areaction chamber of a plasma processing apparatus. The top plateincludes through openings aligned with the apertures in the backingmember. Second fastener members can each be received in an opening ofthe top plate and an aligned aperture of the backing member, andattached to a first fastener member to attach the backing member to thetop plate.

In a preferred embodiment, the electrode assembly is a showerheadelectrode assembly.

A preferred embodiment of a method of making a component for a plasmaprocessing apparatus comprises securing a first part, such as a backingmember to a second part, such as an electrode. The first part includes aplurality of apertures including a first portion and a wider secondportion. A first fastener member is mounted in each aperture. The firstfastener members preferably include a head in the second portion of theaperture. The head is preferably configured to prevent the firstfastener member from being pulled out of the aperture, or from rotating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an upper electrode assembly and a lower electrode for aplasma reaction chamber.

FIG. 2 depicts a fastener including a helicoil used in an upperelectrode assembly.

FIG. 3 depicts a preferred embodiment of an upper electrode assemblyincluding a fastener member with a T-nut.

FIG. 4 is a perspective view of a T-nut.

FIG. 5 is a bottom plan view of a preferred embodiment of an upperelectrode assembly with the electrode removed to show the backingmember.

FIG. 6 is a cross-sectional view in the direction of line 6-6 in FIG. 5.

FIG. 7 is a cross-sectional view in the direction of line 7-7 in FIG. 5.

FIG. 8 is a bottom plan view of a preferred embodiment of an upperelectrode assembly with the electrode removed to show an exemplarypattern of fastener members.

FIG. 9 depicts an aperture in a backing ring.

FIG. 10 depicts another preferred embodiment of an upper electrodeassembly.

DETAILED DESCRIPTION

Components for plasma processing apparatuses are provided. In apreferred embodiment, the component is an electrode assembly for aplasma processing apparatus. The electrode assembly can include abacking member secured to an electrode.

The electrode can be secured to the backing member by a bondingtechnique. The bonding material can be a thermally and electricallyconductive bonding material, such as an elastomer that provides thermaland electrical attachment of the electrode material to the backingmember. The use of elastomers for bonding surfaces together isdescribed, for example, in commonly-owned U.S. Pat. No. 6,073,577, whichis incorporated herein by reference in its entirety.

The electrode preferably is a solid or a perforated plate of singlecrystal silicon. The electrode can optionally have through gas passageswhen used as a showerhead electrode. The backing member is preferably aplate of a material that is chemically compatible with process gasesused in the plasma processing chamber, has a coefficient of thermalexpansion closely matching that of the electrode material, and iselectrically and thermally conductive. Suitable materials for making thebacking member include graphite and SiC, for example.

In another preferred embodiment of the electrode assembly, the backingmember is attached to a top plate.

FIG. 1 depicts a preferred embodiment of an upper electrode assembly 10,which comprises an upper electrode preferably including an innerelectrode member 12, and an outer electrode member 14. A lower electrode15 is shown positioned below the upper electrode. In an embodiment, theinner electrode member 12 is preferably a cylindrical plate. The outerelectrode member 14 can be continuous member (e.g., a poly-siliconmember, such as a ring), or can alternatively include multiple segments(e.g., 2-6 segments). In embodiments including a multiple-segment outerelectrode member 14, contiguous segments preferably overlap each otherto protect the underlying joint, such as an elastomeric joint, fromexposure to plasma.

The upper electrode can be electrically grounded, or it can be poweredwith radio-frequency (RF) current. The upper electrode can be ashowerhead electrode with multiple gas passages for injecting a processgas into a plasma reaction chamber containing the upper electrode andlower electrode 15. The upper electrode assembly 10 and the lowerelectrode 15 can be used in various plasma processing operations, suchas dry etching, chemical vapor deposition, ion implantation, and resiststripping, in the reaction chamber.

Single crystal silicon is a preferred material for plasma exposedsurfaces of the inner electrode member 12 and of the outer electrodemember 14. High-purity, single crystal silicon minimizes contaminationof semiconductor substrates during plasma processing because itintroduces a minimal amount of undesirable elements into the reactionchamber, and also wears smoothly during plasma processing, therebycreating very few particles. Other materials that can be used forplasma-exposed surfaces of the upper electrode include SiC, SiN, AlN,and Al₂O₃, for example.

The backing member preferably includes a backing plate 18, which isco-extensive with the inner electrode member 12, and an outer backingring 22. The backing member is preferably made of graphite. The topsurface 16 of the inner electrode member 12 is preferably bonded to thebacking plate 18, and the top surface 20 of the outer electrode member14 is preferably bonded to a continuous backing ring 22.

The backing plate 18 and backing ring 22 are attached to a top plate 24.The top plate 24 is preferably temperature controlled by flowing a heattransfer fluid (liquid or gas) through it. The top plate 24 ispreferably made of a metal having suitable thermal conductivity, such asaluminum, or an aluminum alloy. The top plate 24 preferably provides anelectrical ground and a heat sink for the electrode. Preferably, avacuum seal is provided between the top plate 24 and the backing plate18 and/or backing ring 22. For example, a sealing member, such as asealing ring 26, can be located between the backing plate 18 and the topplate 24 to minimize gas leakage through an interface between the innerelectrode member 12 and the outer electrode member 14.

In the embodiment shown in FIG. 1, the backing plate 18 and backing ring22 are attached to the top plate 24 by fastener members 28. The fastenermembers 28 can be threaded screws, bolts, or the like. The fastenermembers 28 are inserted from the top surface 30 of the top plate 24 intoopenings 32 and aligned apertures in the backing plate 18 and backingring 22. FIG. 2 shows an embodiment in which the top plate 24 isattached to the backing ring 22 by helicoils 34 inserted in apertures 36in the backing ring 22 (the backing plate 18, inner electrode member 12,and overlying portion of the top plate 24 are not shown for simplicity).The helicoils 34 increase the strength of the threaded connection withthe fastener members 28, as graphite is brittle and has low shearstrength. Gas leakage at the apertures 36 can be minimized by a coverplate (not shown) covering the openings 32. The top plate 24 is shownattached to the backing ring 22 in FIG. 2; however, the same mountingarrangement can be used to attach the backing plate 18 to the top plate24.

It has been determined that the helicoils 34 are prone to pull out ofthe backing plate 18 and backing ring 22 at low bolt torque duringassembly. Also, the helicoils 34 can back out of the apertures 36 whenthe fastener members 28 are removed.

A stronger connection between the electrode assembly 10 and the topplate 24 is provided by first and second fastener members, where aportion of one of the fastener members faces a bearing surface of thebacking member. FIGS. 3 and 4 show a preferred T-nut configuration of afirst fastener member 38. FIGS. 5-7 show further views of the fastenermember 38. The fastener member 38 preferably includes a head 40, shaft42, and internal threads 44. The threads 44 engage with the threads of asecond fastener member 28 when the backing member is attached to the topplate 24.

As shown in FIG. 9, the apertures 36 in the backing plate 18 and in thebacking ring 22 preferably have a stepped configuration, and include afirst portion 37 and a wider second portion 45. The second portion 45 ispartially defined by a bearing surface 47. The head 40 of the fastenermember 38 is sized to fit into the second portion 45 of the aperture 36formed in the backing plate 18, and the second portion 45 of theaperture 36 formed in the backing ring 22. In embodiments in which thegas injection holes of the upper electrode are vertical, the fastenermember 38 preferably is aligned in the direction of the gas injectionholes.

Other aperture configurations than a stepped aperture shown in FIG. 9can alternatively be used. Such other configurations includemultiple-stepped apertures, tapered apertures, and the like. Thecross-section of the apertures 36 can be semi-circular, circular,polyhedral, or have other non-circular configurations. Preferably, theapertures 36 are shaped to match the shape of the fastener members 38 toprevent rotation of the fastener members 38 when they are inserted inthe apertures 36.

In the embodiment shown in FIG. 4, the head 40 of the fastener member 38has at least one transverse dimension, d, which exceeds the maximumtransverse dimension (e.g., the diameter) of the first portion 37 of theaperture 36. The configuration of the head 40 prevents the fastenermember 38 from being pulled out of the aperture 36 toward the top plate24. Consequently, the fastener member 38 provides a significantlygreater pull-out force than the helicoil 34. Also, because the head 40prevents the fastener member 38 from turning in the aperture 36, thefastener member 38 does not back out of the aperture 36 when thefastener member 28 is disengaged from the fastener member 38.

To prevent rotation of the fastener member 38, the head 40 preferablyhas a non-circular shape. The second portion 45 of the aperture 36preferably is shaped to mate with the head 40 when T-nuts are used asthe fastener member 38. The configuration of the head 40 provides abearing surface 48 facing the bearing surface 47 of the second portion45. This arrangement increases the failure bolt force, and preventsrotation of the fastener member 38 relative to the backing plate 18 andthe backing ring 22 when the head 40 is received in the second portion45 of the aperture 36.

The fastener member 38 is not limited to a T-nut configuration. The head40 of the fastener member 38 can alternatively have other non-circularshapes, such as semi-circular, D-shaped, oval, polygonal shapes,including triangular, rectangular, square, trapezoidal, hexagonal, andthe like. For such other shapes, the second portion 45 of the apertures36 in the backing plate 18 and in backing ring 22 preferably have amatching shape to prevent rotation of the fastener member 38 relative tothe backing plate 18 and to the backing ring 22.

Alternatively, the head 40 can have a circular shape, but also include akey in the axial direction, which is received in a mating portion of theaperture 36.

In another embodiment, the head 40 of the fastener member 38 can becircular and non-concentric with respect to the shaft 42. Suchconfiguration prevents rotation of the fastener member 38 in the matingaperture.

The upper electrode assembly can include fastener members 38 having thesame, or a different, head configuration from each other.

The aperture 36 can be formed in the backing plate 18 and in the backingring 22 by any suitable technique, such as milling, drilling, casting,molding, and the like. If desired, the backing plate 18 can include twoor more layers bonded together, with each layer including an aperturecorresponding to a portion of the aperture 36.

In a preferred embodiment, the fastener member 38 is bonded to thebearing surface 47 using an adhesive, such as an elastomer, or the like.The adhesive prevents the fastener member 38 from coming out of therecess 44 during assembly, and also provides a cushion to spread thebearing and torsional loads. After the backing plate 18 and backing ring22 have been bonded to the inner electrode member 12 and outer electrodemember 14, respectively, the fastener member 38 is trapped between theupper electrode and backing member.

The fastener member 38 can be made of any suitable material. Thefastener member 38 can be made of metals and metal alloys including, forexample, stainless steels, such as Nitronic-60, or molybdenum.Nitronic-60 provides resistance to galling in a vacuum environment.Molybdenum has a coefficient of thermal expansion that closely matchesthe coefficient of thermal expansion of graphite, which is preferablyused for the backing plate 18 and backing ring 22. Alternatively, thefastener member 38 can be made of a non-metallic material, such as aceramic, polymer, or composite.

FIG. 8 is a bottom view of the upper electrode assembly 10 with theinner electrode member 12 and the outer electrode member 14 removed toshow an exemplary concentric arrangement of fastener members 38installed in the backing plate 18 and backing ring 22. The upperelectrode assembly 10 preferably includes from about 8 to 32 fastenermembers 38. Concentrically arranged gas injection holes 48 formed in thebacking plate 18 are also shown in FIG. 8. The gas injection holes 48are preferably aligned with gas passages in the inner electrode member12.

FIG. 10 depicts another preferred embodiment of an upper electrodeassembly including an alternative fastening arrangement. A fastenermember 128 is received in an aperture 136 in the backing ring 22, and inan opening 132 in the top plate 24 (the backing plate 18, innerelectrode member 12, and associated portion of the top plate 24 are notshown for simplicity). The fastener member 128 includes a head 129 and ashaft 130. The shaft 130 preferably includes external threads 131 at anupper portion 131. A fastener member 140, such as a threaded nut,engages the threads 131 to secure the top plate 24 to the backing ring22 and to the outer electrode member 14.

In the embodiment shown in FIG. 10, the fastener member 128 preferablyis bonded to a bearing surface 147 of the backing ring 22 with asuitable adhesive, as described above.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

1. A method of making an electrode assembly for a plasma processingapparatus, comprising: mounting a plurality of first fastener members ina plurality of apertures of a backing member, each aperture including afirst portion and a second portion wider than the first portion, eachfirst fastener member including a head disposed in the second portion ofan aperture; bonding the head of each of the first fastener members to abearing surface that partially defines the second portion of theaperture; and securing the backing member to an electrode; the head ofeach of the first fastener members being configured to prevent the firstfastener members from being pulled out of the respective apertures in adirection away from the electrode or from rotating.
 2. The method ofclaim 1, further comprising fastening the backing member to a top plateincluding a plurality of through openings each of which is aligned witha respective aperture of the backing member, the fastening includinginserting a second fastener member in openings of the top plate suchthat each second fastener member engages a respective first fastenermember to secure the backing member to the top plate.
 3. The method ofclaim 1, wherein the first fastener members are T-nuts.
 4. The method ofclaim 3, wherein each of the T-nuts has internal threads, and the secondfastener member comprises a bolt threaded into a respective one of theT-nuts.
 5. The method of claim 2, wherein the head is a rectangularshaped head and the second portion of the apertures is rectangular inshape.
 6. The method of claim 2, wherein the electrode comprises aninner silicon electrode and an outer silicon electrode comprised ofoverlapping contiguous segments, the backing member comprising a plateadhesively bonded to the inner silicon electrode and a ring adhesivelybonded to the outer silicon electrode.
 7. The method of claim 2, whereinthe electrode comprises a showerhead electrode having gas passages andthe backing member comprises a backing plate having gas injection holes,the method further comprising bonding the showerhead electrode to thebacking plate with the gas injection holes of the backing plate alignedwith the gas passages of the showerhead electrode.
 8. The method ofclaim 2, wherein the electrode comprises a showerhead electrode and thefirst fastener members comprise a plurality of fastener membersconcentrically arranged at locations between adjacent rows of gaspassages in the showerhead electrode.